use v6-alpha;

say "1..2";

multi foo ($only_one_arg) {
    if $only_one_arg eq "only_one_arg"     { say "ok 1" } else { say "not ok 1" }
}

multi foo ($arg1, $arg2) {
    if $arg1 eq "arg1" and $arg2 eq "arg2" { say "ok 2" } else { say "not ok 2" }
}

foo "only_one_arg";
foo "arg1", "arg2";